Characterizing counter-streaming interpenetrating plasmas relevant to astrophysical collisionless shocks

A series of Omega experiments have produced and characterized high velocity counter-streaming plasma flows relevant for the creation of collisionless shocks. Single and double CH₂ foils have been irradiated with a laser intensity of ∼ 10¹⁶ W/cm². The laser ablated plasma was characterized 4 mm from the foil surface using Thomson scattering. A peak plasma flow velocity of 2000 km/s, an electron temperature of ∼ 110 eV, an ion temperature of ∼ 30 eV, and a density of ∼ 10¹⁸ cm ^-3 were measured in the single foil configuration. Significant increases in electron and ion temperatures were seen in the double foil geometry. The measured single foil plasma conditions were used to calculate the ion skin depth, c/ω_pi ∼ 0.16 mm, the interaction length, l_int, of ∼ 8 mm, and the Coulomb mean free path, λ_mfp ∼ 27 mm. With c/ω_pi ≪ l _int ≪λ_mfp, we are in a regime where collisionless shock formation is possible.